In recent years, a reproducing apparatus has come to be widely used in which the digital audio signal and the digital video signal recorded in compressed form in various recording media such as CD-ROM, DVD-ROM and hard disk are read and decompressed, and the decompressed signal is reproduced through a display and a speaker or the like connected thereto.
An apparatus for recording and reproducing the digital audio signal and the digital video signal in compressed form for the BS digital broadcast, the CS digital broadcast, the digital terrestrial broadcast or the like has also come to be widely used.
MPEG is known as a standard for coding and compressing the audio signal and the video signal into a digital signal and subsequently decoding the signal. In MPEG, the multiplexed and compression-coded audio signal and video signal are decoded, after which the audio signal and the video signal are reproduced in synchronism with each other. For this purpose, information (hereinafter referred to as the “time information”) on the time of execution of the signal reproduction and display is added to each of the audio signal and the video signal at the time of coding, and then the signals are compressed. As a result, in the case where the compression-coded digital audio signal and video signal are decompressed, the reproducing apparatus reproduces the audio signal and the video signal in synchronism with each other by referring to the time information based on the system time clock value contained in the reproducing apparatus.
A conventional reproducing method is explained below. Note that the applicant acknowledges the method of reproducing the image and the sound disclosed in Patent Document 1, and to clarify the problem to be solved by the present invention, the reproducing method disclosed in Patent Document 1 is explained briefly as a prior art. According to this method, in order to reproduce first and second images having different imaging angles, a video signal corresponding to each angle is decoded by being inputted in a different video decoding unit and the images decoded independently of each other are combined and displayed on a single screen. As to the audio signal, plural audio signals are similarly reproduced by being decoded at the same time by different audio decoding means independently of each other.
The conventional audio reproducing method is explained below with reference to FIG. 1. FIG. 1 is a block diagram showing a configuration of a dual audio decoder 183 for carrying out the reproducing method. With reference to FIG. 1, a specific configuration of the dual audio decoder 183 is explained. The dual audio decoder 183 includes a first audio decoder 183a, a second audio decoder 183b, a first audio selection circuit 183c and a second audio selection circuit 183d. In the case where two audio signals of Japanese and English are reproduced at the same time, for example, the first audio signal constituting the signal of the voice in Japanese is inputted to the first audio decoder 183a and decoded. At the same time, the second audio signal constituting the signal of the voice in English is inputted to the second audio decoder 183b and decoded.
The first and second audio signals thus decoded are processed by the first audio selection circuit 183c and the second audio selection circuit 183d. In the case where one each of left and right channels are available as audio output channels, for example, the first and second audio signals are processed so as to be outputted through one channel each in monaural mode, or only one of the first and second audio signals is processed to be outputted in two-channel stereo. In the case where the audio output channels are more than one each of left and right channels, the first and second audio signals are processed to be outputted in a combination of stereo and monaural modes and the like.
Further, with regard to the audio data of (5+1) channel configuration of Dolby digital system, the first audio selection circuit 183c and the second audio selection circuit 183d can output two channels each in stereo for (5+1) channels that can be outputted or can selectively output only the (5+1) channels of one of the audio data.
Patent Document 1: Japanese Laid-Open Patent Application No. Hei 10-145735 (pp. 10-11, FIGS. 4, 8 and 9)